Dynamics and courses of beaver (Castor fiber L.) expansion in Croatia

摘要

The beaver population brought over from Bavaria and inhabited in Croatia in the period from 1996-1998 has successfully adapted to its new habitat and hence, in the previous period, a very successful reproduction and spatial expansion has been noticed. While choosing a site for releasing beavers, it was presumed that beavers would expand downstream, so that sites were chosen in the upper part of the area envisaged as their future natural site (habitat). Previous beaver monitoring showed that the highest percentage of beaver expansion direction is upstream from the place where they had been released, plus a partly combined upstream and downstream direction, and downstream only to a lesser extent. Having analysed the distances covered by beavers while they were looking for new sites which they are currently inhabiting, it has been noticed that certain families have covered huge distances from the place of their release or earlier stay, leaving along the covered distances numerous sites suitable for their lodging. Distances between certain sites presently inhabited by beavers and their place of release are even up to 300 km, observed based on the length of the watercourse through which they moved to their new destination. Taking into consideration previous results of beaver monitoring in Croatia, it may be concluded that in the next ten-year period the beavers will spread from watercourses and water areas in the western part of Croatia, i.e. river sources, to the eastern part, i.e. to the Danube. The area which is at the beavers' disposal and where they still have not been registered are the watercourses and waters of the eastern part of Croatia in the Sava and the Drava basins. In order for them to inhabit that area, their expansion will have to move in downstream direction, which was less present in the previous research.%Populacija dabrova naseljenih u Hrvatsku iz Bavarske u razdoblju od 1996 - 1998 godine uspješno se prilagodila novom staništu te je u dosadašnjem razdoblju zamijećena vrlo uspješna reprodukcija i prostorno širenje. Tijekom odabira lokaliteta za ispuštanje dabrova pretpostavljalo se da će se dabrovi širiti nizvodno pa su lokaliteti odabrani u gornjem dijelu područja koje je predviđeno kao buduće stanište. Dosadašnji monitoring dabrova pokazao je da je smjer širenja dabrova u većem postotku uzvodno od mjesta ispuštanja, dijelom kombinirano nizvodno i uzvodno a manjim dijelom samo nizvodno. Analizirajući udaljenosti koje su dabrovi prevalili u potrazi za novim lokalitetima koje danas nastanjuju zamijećeno je da su pojedine familije prevalile velike udaljenosti od mjesta ispuštanja ili ranijeg nastanjivanja, ostavljajući na prevaljenoj udaljenosti brojne lokalitete pogodne za njihovo obitavanje. Udaljenosti pojedinih lokaliteta koje danas nastanjuju dabrovi od mjesta ispuštanja, kreću se čak do 300 km promatrano dužinom vodotoka kojim su se kretali do novog odredišta. Uvažavajući dosadašnje rezultate praćenja dabrova u Hrvatskoj može se zaključiti da će u predstojećem desetogodišnjem razdoblju dabrovi nastaniti vodotoke i vodene površine od zapadnog dijela Hrvatske odnosno izvorišta rijeka i potoka pa do istočnog dijela odnosno do Dunava.